Semiconductor processes use vapor precursors for processing of thin films on an integrated circuit (IC) substrate. The majority of these vapor precursors, together with their by-products, are pumping out and exhausted to a waste stream.
It is very expensive to collect and dispose of the precursor exhaust products. Further, these non-reactive precursors and these byproducts can be hazardous and harmful to the environment. The IC industry is forced to conform to ever more stringent regulations concerning the storage and disposal of these wastes.
It is inconvenient to collect waste as a gas because it is difficult to transport and voluminous to store. It is more convenient to convert the waste, at least partially, into a solid or liquid form. The use of cold traps to completely condense some chemical vapors is well-known. It is also well known to use cold traps to condense elements of a precursor at least to simplify the waste collection process.
In a chemical vapor deposition (CVD) process, high temperature process is often used. Because of the low efficiency of the CVD process, a hot trap is recommended for completing the CVD reaction, leaving only the by-products to the exhaust stream. An example is copper CVD process. Copper CVD process uses copper-hfac-tmvs precursor to deposit copper on a hot surface (˜200° C.) following the reaction:2 Cu-hfac-tmvs→Cu+Cu(hfac)2+2 tmvs (at >˜100° C.)
The reaction occurs at a temperature higher than ˜100° C. The efficiency of this reaction is roughly 10–20%; thus 80–90% of the precursor leaves the process chamber un-reacted. A cold trap would then collect the precursor Cu-hfac-tmvs, and the by-products Cu(hfac)2 and tmvs. Using a hot trap before the cold trap, most of the precursor would further react, leaving only the by-products in the waste stream.
FIG. 1 shows a prior art apparatus for such a recovery and abatement of CVD copper process. Precursor exhaust leaves the process chamber 10, encounters the hot trap 20 to further the reaction. The vacuum pump 30 then pumps away the precursor exhaust. The exhaust then encounters the cold trap 40 to trap all precursor by-products which then drop into the drain 45. The vacuum pump is located after the hot trap to avoid deposition inside the pump, thus prolong the pump life.
The major disadvantage of this prior art is the potential contamination of the process chamber due to the hot trap. With the hot trap raising the efficiency from 10–20% to 100%, the amount of by-products Cu(hfac)2 and tmvs will increase 3–5 times, increasing the potential contaminants products, in this case Cu(hfac)2 and tmvs, 3–5 times. Also the efficiency of the hot trap is low because of the low pressure inside the hot trap, and the hot and cold traps would be two separate units. However, the prior art recommends using this configuration to avoid damage to the vacuum pump.
It would be advantageous if hot and cold traps could be combined in a single system to collect different types of wastes from an exhausted chemical vapor.
It would be advantageous if a multi-stage trapping system could be provided that operated at a high pressure so that the chemical reactions in the traps are efficient.